One of the problems encountered in conventional incinerator design is the heat buildup in the combustion chamber. During the course of the combustion process, the air inlet conduit through which air is introduced into the combustion chamber becomes heated, resulting in the combustion air expanding and slowing the burning rate. This design problem, is commonly referred to as "burndown".
Ash removal problems have also been encountered with the conventional commercial or industrial-type incinerator. In certain types of incinerators, it is necessary to shut down the combustion in order to manually remove the ash from the combustion chamber and this downtime adversely affects the overall efficiency of the incinerator.
In other incinerators, conveyors have been employed in the lower end of the combustion chamber, which when operated, serve to convey the ash from the combustion chamber to a discharge site. However, due to the intense heat generated in the combustion chamber, the conveyors rapidly deteriorate, thereby requiring substantial maintenance.
In larger commercial incinerators, grates are employed and periodically the grates are agitated to drop the ash to a conveyor system located beneath the grates. However, the grates can become clogged with clinkers and non-combustible materials, and the mechanism for operating the grates is expensive.
Further difficulties have been experienced in incinerator design in achieving complete combustion of the combustible waste material. In order to increase the efficiency of the combustion and reduce the discharge of pollutants into the atmosphere, the incinerator often includes a secondary zone of combustion in the stack, where air is delivered to the stack to burn the combustible waste gases.
Recently, with the increased use of plastic materials, it has been found that the conventional incinerator system is not totally effective in preventing the discharge of gaseous pollutants to the atmosphere. This is due to the greater BTU content of the plastic material and the higher temperatures involved in the combustion. In an attempt to provide more effective combustion of plastic materials, attempts have been made to increase the input of gas, or other fuel, to the incinerator. However, the increased rate of combustion has correspondingly increased the velocity of gas flow through the stack. Thus, air introduced into the stack for secondary combustion purposes merely flows along the inner wall of the stack without adequately mixing with the waste gases, which flow upwardly along the central portion of the stack. The result is a "candlestick" effect, with the air flowing along the refractory wall of the stack and the waste gases flowing along the central core. The laminar flow of the air and gas prevents adequate mixing of the air with the waste gases, with the result that incomplete combustion is obtained.